1. Field of the Invention
The invention relates generally to an assay device with multiple capture zones located substantially equidistant from a sample receiving area, and arranged in a linear array perpendicular to the sample path out of the sample receiving area. More particularly, the sample contacts each one of the multiple capture zones without passing through another capture zone thereby allowing for efficient testing for multiple target analytes in a single sample.
2. Description of the Related Art
Various lateral flow assay methods are utilized to test for the presence or, absence, or quantity of an analyte in a biological sample. A “sandwich” assay method, for example, uses an antibody immobilized on a solid support, which forms part of a sandwich with a labeled antibody, to determine the presence of a target analyte by observing the presence and amount of bound analyte-labeled antibody complex. In a competition assay, antibody is bound to a solid surface and then contacted with a sample containing both an unknown quantity of antigen analyte and labeled antigen of the same type. An indirect measure of the concentration of antigen analyte in the sample is provided by the measured amount of labeled antigen bound to the solid support. Numerous assay methods such as these may be performed on a lateral flow test strip.
Conventional lateral flow test strips feature a solid support on which the sample receiving area and the target capture zones are supported. The solid support material is one which is capable of supporting the sample receiving area and target capture zones and providing for the capillary flow of sample out from the sample receiving area to the target capture zones when the lateral flow test strip is exposed to an appropriate solvent or buffer which acts as a carrier liquid for the sample. General classes of materials which may be used as support include organic or inorganic polymers, and natural and synthetic polymers. More specific examples of suitable solid supports include, without limitation, glass fiber, cellulose, nylon, crosslinked dextran, various chromatographic papers and nitrocellulose. One particularly preferred material is nitrocellulose. See, for instance, U.S. Pat. Nos. 6,267,722, 5,654,162, 5,591,645 and 4,703,017.
Traditional lateral flow test strips contain one or more target capture lines. These capture lines are located on the strip parallel with the sample receiving area such that the flow of the sample from a sample receiving area sequentially contacts each of the capture lines. Sample aliquots are deposited onto a sample receiving area of the lateral flow test strip which may then be exposed to a solvent or carrier liquid which flows across the strip, and carries the sample material across the target capture zones toward an absorbent pad located at the end of the test strip. These features are illustrated in FIG. 1 with a lateral flow test strip with the various capture lines aligned parallel to the sample receiving area and the flow of the sample out of the sample receiving area contacting sequentially each capture line. The conventional lateral flow test strips are constructed for use with commercially available readers and thus are sized to fit in a specific sized plastic housing. The housing typically has an upper part with an opening for sample application to the sample pad and another opening or window over the capture lines to read the results of the assay.
There is a limit to the number of target capture lines that can be used with the conventional lateral flow assay format. The limit arises, in part, because succeeding capture lines, located further away from the sample pad, suffer from the non-specific capture of sample and analyte by the preceding capture zones and the materials used to construct the assay device. This non-specific capture, which also occurs in the assay strip material itself, results in the sample supply becoming exhausted prior to contacting all target capture lines. Locating target capture zones further away from the sample receiving area decreases signal intensity. This loss of signal intensity may then affect sensitivity. Clearly there is a need to minimize the occurrence and effects of non-specific analyte capture on a lateral flow test strip.
One lateral flow assay technique of particular interest is the UPT-LF (Upconverting Phosphor Technology-Lateral Flow) assay method which utilizes up-converting phosphor microparticles as labels on lateral flow test strips. The UPT-LF technology may be utilized in, for instance, sandwich or competitive formats for the analysis of, for instance, drugs, drug metabolites, or other substances, such as, antigens, proteins, and DNA. It has been shown (Corstjens et al., Clin. Chem., 2001, 47, pp. 1885-1893; Corstjens et al., Anal. Biochem., 2003, 312, pp. 191-200, 2003; Zuiderwijk et al. Clin. Biochem., 2003, 36, pp. 401-403) that besides the conventional antibody-antigen UPT-LF assays, nucleic acid UPT-LF assays have also been developed. Clearly, the possible detection of both proteins and nucleic acids from one sample on one lateral flow test strip is likely to further increase complexity of the assay, the sample and the lateral flow capture zones. Thus, there is a need for an assay strip which easily permits more numerous analyses in a single test.